Effect of regular smoking on flicker induced retinal vasodilatation in healthy subjects

Effects of firsthand tobacco smoking on retinal vessel caliber: a systematic review and meta-analysis

PURPOSE

To review the effects of firsthand tobacco smoking on central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) of firsthand tobacco smokers.

METHODS

We performed a search on EMBASE and PubMed for studies up to 15th July 2022. Two independent reviewers selected studies with baseline data of CRAE and CRVE of current smokers, nonsmokers, and former smokers. Initial search identified 893 studies, of which 10 were included in the meta-analysis. Two independent reviewers extracted data from the included studies. The quality of studies was assessed by the Newcastle-Ottawa Scale.

RESULTS

In this meta-analysis, 7431 nonsmokers, 2448 current smokers and 5786 former smokers, as well as 7404 nonsmokers, 2430 current smokers and 5763 former smokers were included in CRAE and CRVE analysis respectively. Nonsmokers had narrower CRVE (Weighted mean difference [WMD], -12.15; 95% CI, -17.33 - -6.96) and CRAE (WMD, -4.77; 95% CI, -7.96 - -1.57) than current smokers, and narrower CRVE (WMD, -3.08; 95% CI, -6.06 - -0.11) than former smokers. Current smokers had wider CRVE (WMD, 10.42; 95% CI, 7.80 - 13.04) and CRAE (WMD, 7.05; 95% CI, 6.65 - 7.46) than former smokers. Subgroup analysis and sensitivity analysis were performed.

CONCLUSION

Firsthand tobacco smoking resulted in wider CRAE and CRVE in current and former smokers, particularly in CRVE, and such changes may not be reversible after smoking cessation. Therefore, retinal vessel caliber may reflect the effects of firsthand tobacco smoking and be used to estimate the risk of cardiovascular diseases.

Secondhand smoke exposure and ocular health: A systematic review

The toxicology of secondhand smoke (SHS), along with the harm of its exposure to human health, has been generally acknowledged; however, specific evidence is lacking on the association between SHS exposure and ocular health. In this systematic review (PROSPERO registration number: CRD42022247992), we included 55 original articles published by 12 May 2023, which dealt with SHS exposure and ocular disorders, such as eye irritation, conjunctivitis, dry eye diseases, uveitis, myopia, astigmatism, contact lens discomfort, age-related macular degeneration, glaucoma, and thyroid eye disease that addressed the ocular neurovascular structures of the macular, retinal nerve fiber layer, choroid, and corneal biomechanical parameters. We found compelling correlational evidence for eye irritation, conjunctivitis, and dry eye symptoms-supporting that SHS exposure was positively associated with inflammatory and allergic changes in the eyes. Yet, evidence about the associations between SHS exposure and other ocular disorders, structures, and parameters is still limited or controversial. Given the limitations of existing literature, more investigations with high quality and rigorous design are warranted to elucidate the potentially harmful effects of SHS exposure on ocular health.

Methods to measure blood flow and vascular reactivity in the retina

Disturbances of retinal perfusion are involved in the onset and maintenance of several ocular diseases, including diabetic retinopathy, glaucoma, and retinal vascular occlusion. Hence, knowledge on ocular vascular anatomy and function is highly relevant for basic research studies and for clinical judgment and treatment. The retinal vasculature is composed of the superficial, intermediate, and deep vascular layer. Detection of changes in blood flow and vascular diameter especially in smaller vessels is essential to understand and to analyze vascular diseases. Several methods to evaluate blood flow regulation in the retina have been described so far, but no gold standard has been established. For highly reliable assessment of retinal blood flow, exact determination of vessel diameter is necessary. Several measurement methods have already been reported in humans. But for further analysis of retinal vascular diseases, studies in laboratory animals, including genetically modified mice, are important. As for mice, the small vessel size is challenging requiring devices with high optic resolution. In this review, we recapitulate different methods for retinal blood flow and vessel diameter measurement. Moreover, studies in humans and in experimental animals are described.

Neuro-vascular coupling and heart rate variability in patients with type II diabetes at different stages of diabetic retinopathy

Aims/Hypothesis

There is evidence that diabetes is accompanied by a break-down of functional hyperemia, an intrinsic mechanism of neural tissues to adapt blood flow to changing metabolic demands. However, to what extent functional hyperemia is altered in different stages of diabetic retinopathy (DR) in patients with type II diabetes is largely unknown. The current study set out to investigate flicker-induced retinal blood flow changes in patients with type II diabetes at different stages of DR.

Materials and methods

A total of 76 subjects were included in the present parallel-group study, of which 56 had diabetes with either no DR or different stages of non-proliferative DR (n = 29 no DR, 12 mild DR, 15 moderate to severe DR). In addition, 20 healthy subjects were included as controls. Retinal blood flow was assessed before and during visual stimulation using a combined measurement of retinal vessel calibers and blood velocity by the means of Doppler optical coherence tomography (OCT). To measure systemic autonomic nervous system function, heart rate variability (HRV) was assessed using a short-term orthostatic challenge test.

Results

In healthy controls, retinal blood flow increased by 40.4 ± 27.2% during flicker stimulation. Flicker responses in patients with DR were significantly decreased depending on the stage of the disease (no DR 37.7 ± 26.0%, mild DR 26.2 ± 28.2%, moderate to severe DR 22.3 ± 13.9%; p = 0.035, ANOVA). When assessing systemic autonomous neural function using HRV, normalized low frequency (LF) spectral power showed a significantly different response to the orthostatic maneuver in diabetic patients compared to healthy controls (p < 0.001).

Conclusion/Interpretation

Our study indicates that flicker induced hyperemia is reduced in patients with DR compared to healthy subjects. Further, this impairment is more pronounced with increasing severity of DR. Further studies are needed to elucidate mechanisms behind the reduced hyperemic response in patients with type II diabetes.

Clinical trial registration

[https://clinicaltrials.gov/], identifier [NCT03 552562].

Longitudinal Study of Optic Disk Perfusion and Retinal Structure in Leber's Hereditary Optic Neuropathy

Purpose

The purpose of this study was to evaluate optic disk perfusion and neural retinal structure in patients with subacute Leber's hereditary optic neuropathy (LHON) and LHON carriers, as compared with healthy controls.

Methods

This study included 8 patients with LHON in the subacute stage, 10 asymptomatic carriers of a LHON-associated mitochondrial DNA mutation, and 40 controls. All subjects underwent measurement of the retinal nerve fiber layer (RNFL) thickness, the ganglion cell-inner plexiform layer (GCIPL) thickness using optical coherence tomography and optic disk microvascular perfusion (Mean Tissue [MT]) using laser speckle flowgraphy (LSFG). Patients were re-examined after a median interval of 3 months from the baseline visit.

Results

LHON carriers had higher values of RNFL thickness, GCIPL thickness, and disk area than controls (P < 0.05), whereas MT was not different between the two groups (P = 0.936). Median MT and RNFL thickness were 32% and 15% higher in the early subacute stage of the disease than in controls (P < 0.001 and P = 0.001). MT declined below the values of controls during the late subacute stage (P = 0.024), whereas RNFL thickness declined later during the dynamic stage (P < 0.001). GCIPL thickness was lower in patients with LHON than in controls independently of the stage of the disease (P < 0.001).

Conclusions

The high blood flow at the optic disk during the early subacute stage may be the consequence of vasodilation due to nitric oxide release as compensation to mitochondrial impairment. Optic disk perfusion as measured by LSFG is a promising biomarker for LHON diagnosis and monitoring as well as an objective outcome measure for assessing response to therapies.

Retinal Microvascular Reactivity in Chronic Cigarette Smokers and Non-smokers: An Observational Cross-Sectional Study

Purpose: To evaluate the changes in the retinal microvasculature and its reactivity in chronic cigarette smokers.

Methods: Thirty-four male chronic cigarette smokers and 18 male non-smokers were enrolled. Optical coherence tomography angiography was used to measure the perfused retinal vessel densities (PVDs) of the peripapillary and parafoveal areas at baseline and during phase IV of the Valsalva maneuver (VM-IV). Systemic blood pressure and intraocular pressure were also measured.

Results: The baseline PVD in the peripapillary area of the smokers was significantly lower than the non-smokers (59.56 ± 2.26% vs. 61.67 ± 3.58%, respectively; P = 0.005). However, there was no significant difference in the foveal avascular zone or parafoveal PVD between the two groups. During VM-IV, the peripapillary PVD of the smokers decreased by 1.13 ± 3.50%, which was significantly less than that of the non-smokers (−3.83 ± 4.26%, P < 0.05). Similarly, the parafoveal PVD of the smokers decreased by 5.49 ± 9.70%, which was significantly less than the percentage change of the non-smokers (−13.01 ± 8.39%, P < 0.05). There was no significant difference in the percentage change in systemic blood pressure parameters between the two groups.

Conclusion: The retinal microvasculature and its reactivity were impaired in chronic smokers compared with non-smokers. The extent of impairment differed among different regions of the fundus.

Evaluation of subclinical alterations in retinal layers and microvascular structures with OCT and OCTA in healthy young short-term smokers

PURPOSE

To detect the changes that can be determined with optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) in young and short-term smokers.

METHOD

In this cross-sectional, observational, and comparative study, 45 "healthy" smokers and 45 healthy non-smoker control participants were included. Those with a smoking history between 1 year to 5 years and an average of 10-30 cigarettes per day were included in the study. OCT and OCTA measurements were made at least 60 min after smoking and at least 8 h after caffeine-containing beverages in order to end the effect of nicotine on systemic and retinal blood flow in the smoking group.

RESULTS

The mean smoking period was 2.2 ± 0.13 years. Mean macular thickness(MMT), retinal nerve fiber layer(RNFL), and choroidal thickness(Cht) were significantly lower in the smoker group, while ganglion cell-inner plexiform layer(GC-IPL) thickness was higher. Vessel density(VD) values were similar between groups, while perfusion density(PD) values were significantly higher in the smoker group. There were significant correlations between MMT and outer VD, outer PD, foveal avascular zone(FAZ) perimeter and circularity index. FAZ area and central VD and PD were inversely correlated. Also, FAZ circularity index and subfoveal, nasal, and temporal ChTs were positively correlated.

CONCLUSION

Despite the short-term smoking, ischemic effects were observed in retinochoroidal and vascular structures.

Association of Secondhand Smoking Exposure With Choroidal Thinning in Children Aged 6 to 8 Years: The Hong Kong Children Eye Study

Importance

Secondhand smoking is a risk to adult ocular health, but its effect on children's ocular development is not known.

Objective

To assess the association between choroidal thickness and secondhand smoking exposure in children.

Design, Setting, and Participants

Children aged 6 to 8 years were consecutively recruited from January 2016 to July 2017 from the population-based Hong Kong Children Eye Study at the Chinese University of Hong Kong Eye Centre. All participants underwent detailed ophthalmic investigations. Choroidal thickness was measured by swept-source optical coherence tomography, with built-in software that automatically segmented the choroid layer to analyze its terrain imagery. History of secondhand smoking was obtained from a questionnaire. Multiple linear regression analyses were performed to assess the correlation between choroidal thickness and secondhand exposure when controlling for confounding factors. Analysis began July 2018 and ended in April 2019.

Main Outcomes and Measurements

The association between children's choroidal thickness and their exposure to secondhand smoking.

Results

Of 1400 children, 941 (67.2%) had no exposure to secondhand smoking, and 459 (32.8%) had exposure to secondhand smoking. The mean (SD) age was 7.65 (1.09) years for children in the nonexposure group and 7.54 (1.11) years for children in the exposure group. After adjustment for age, sex, body mass index, axial length, and birth weight, exposure to secondhand smoking was associated with a thinner choroid by 8.3 μm in the central subfield, 7.2 μm in the inner inferior, 6.4 μm in the outer inferior, 6.4 μm in the inner temporal, and 7.3 μm in the outer temporal. Choroidal thinning with also associated with increased number of family smokers and increased quantity of secondhand smoking. An increase of 1 family smoker was associated with choroidal thinning by 7.86 μm in the central subfield, 4.51 μm in the outer superior, 6.23 μm in the inner inferior, 5.59 μm in the outer inferior, 6.06 μm in the inner nasal, and 6.55 μm in the outer nasal. An increase of exposure to 1 secondhand cigarette smoke per day was associated with choroidal thinning by 0.54 μm in the central subfield, 0.42 μm in the inner temporal, and 0.47 μm in the outer temporal.

Conclusions and Relevance

This investigation showed that exposure to secondhand smoking in children was associated with choroidal thinning along with a dose-dependent effect. These results support evidence regarding the potential hazards of secondhand smoking to children.

Dry eye disease and retinal nerve fiber layer changes in chronic smokers

Purpose:

To study the effect of smoking on tear film parameters and retinal nerve fiber layer thickness (RNFL) in chronic smokers.

Methods:

This was a cross-sectional study, which included 60 (120 eyes) smokers who have smoked at least 10 pack-year and an equal number of healthy subjects as a control for comparison. In addition to history, a detailed slit-lamp examination was done to evaluate the anterior and posterior segments. All patients underwent Schirmer’s I test (SIT) with Whatman-41 filter paper, tear meniscus height (TMH), and RNFL with a Fourier-domain optical coherence tomography (OCT) and tear film breakup time (TBUT) with 2% fluorescein and cobalt blue filter using slit-lamp biomicroscopy.

Results:

The (mean ± SD) age of the participants was 56.48 ± 10.38 years. There was a statistically significant reduction in tear film parameters in smokers compared to nonsmokers (P = 0.000). The incidence of MGD was found to be higher in smokers when compared to nonsmokers with a P value of 0.000. RNFL in all four quadrants was also significantly reduced in smokers compared to nonsmokers (P = 0.00).

Conclusion:

This study shows that chronic smoking leads to an increased incidence of dry eye disease and is associated with RNFL thinning. Smoking can result in cumulative RNFL loss in patients with ocular neurodegenerative disorder and OCT of these patients may have to be interpreted keeping this in mind.

Blood pressure variability and microvascular dysfunction: the Maastricht Study

BACKGROUND

Microvascular dysfunction (MVD) contributes to stroke, dementia, depression, retinopathy and chronic kidney disease. However, the determinants of MVD are incompletely understood. Greater blood pressure variability (BPV) may be one such determinant.

METHODS AND RESULTS

We used cross-sectional data of The Maastricht Study (n = 2773, age 59.9 years; 51.9% men) to investigate whether greater very short- to mid-term BPV is associated with various MVD measures. We standardized and averaged within-visit, 24-h and 7-day BPV into a systolic and a diastolic BPV composite score. MVD measures included a composite score of MRI cerebral small vessel disease (CSVD) features (total brain parenchymal volume, white matter hyperintensity volume, lacunar infarcts and cerebral microbleeds), a composite score of flicker light-induced retinal arteriolar and venular dilation response, albuminuria, heat-induced skin hyperemia and a composite score of plasma biomarkers of MVD (sICAM-1, sVCAM-1, sE-selectin and von Willebrand Factor). We used linear regression adjusted for age, sex, glucose metabolism status, mean 24-h systolic or DBP, cardiovascular risk factors and antihypertensive medication. We found that higher systolic and diastolic BPV composite scores (per SD) were associated with higher albuminuria [higher ratio, 1.04 (95% CI 1.00-1.08) and 1.07 (1.03-1.11), respectively], but not with other measures of MVD tested.

CONCLUSION

Greater systolic and diastolic BPV was associated with higher albuminuria, but not with CSVD features, flicker light-induced retinal arteriolar and venular dilation response, heat-induced skin hyperemia and plasma biomarkers of MVD. This suggests that the microvasculature of the kidneys is most vulnerable to the detrimental effects of greater BPV.

Retinal vasodilatory responses are inversely associated with plasminogen activator inhibitor-1: The African-PREDICT study

AIMS

Plasminogen activator inhibitor-1 (PAI-1), traditionally associated with fibrinolysis, is increasingly implicated in impaired vascular function. However, studies on its association with microvascular function are limited to the cutaneous and coronary microvascular beds in older and diseased individuals. To better understand its potential involvement in the early stages of disease development, we investigated the associations of retinal vasodilatory responses to flicker light with PAI-1 activity (PAI-1_act) in young and healthy individuals.

METHODS

We included healthy Black and White women and men (n = 518; aged 20-30 years), and measured plasma PAI-1_act and retinal vasodilatory responses to flicker light provocation. We also collected demographic and lifestyle data, measured blood pressure, anthropometry, blood lipids, inflammatory and other biomarkers.

RESULTS

In multivariate regression analyses, maximal retinal venular dilation associated independently and inversely with PAI-1_act (adj. R² = 0.11; β = -0.15; p = 0.001) in the total group. In exploratory subgroup analyses, this association remained in White women (adj. R² = 0.07; β = -0.23; p = 0.005), and was more robust with younger age and lower blood pressure and in non-smokers, but also with greater central adiposity, higher low-density lipoprotein cholesterol and inflammation (all p < 0.05).

CONCLUSIONS

Our data suggest that in young individuals, PAI-1 may already be associated with subclinical microvascular dysfunction.

Carotid stiffness is associated with retinal microvascular dysfunction-The Maastricht study

Objective

This study investigated whether arterial stiffening is a determinant of subtle retinal microvascular changes that precede diabetic retinopathy.

Research design and methods

This study used cross‐sectional data from the Maastricht Study, a type 2 diabetes‐enriched population‐based cohort study. We used multivariable linear regression analysis to investigate, in individuals without and with type 2 diabetes, the associations of carotid distensibility coefficient and carotid‐femoral pulse wave velocity with retinal microvascular diameters and flicker light‐induced dilation and adjusted for cardiovascular and lifestyle risk factors.

Results

The retinal microvascular diameter study population consisted of N = 2434 participants (51.4% men, mean ± SD age 59.8 ± 8.1 years, and 28.1% type 2 diabetes). No measures of arterial stiffness were significantly associated with microvascular diameters. Greater carotid distensibility coefficient (i.e., lower carotid stiffness) was significantly associated with greater retinal arteriolar flicker light‐induced dilation (per standard deviation, standardized beta [95% CI] 0.06 [0.00; 0.12]) and non‐significantly, but directionally similarly, associated with greater retinal venular flicker light‐induced dilation (0.04 [−0.02; 0.10]). Carotid‐femoral pulse wave velocity (i.e., aortic stiffness) was not associated with retinal microvascular flicker light‐induced dilation. The associations between carotid distensibility coefficient and retinal arteriolar and venular flicker light‐induced dilation were two‐ to threefold stronger in individuals with type 2 diabetes than in those without.

Conclusion

In this population‐based study greater carotid, but not aortic, stiffness was associated with worse retinal flicker light‐induced dilation and this association was stronger in individuals with type 2 diabetes. Hence, carotid stiffness may be a determinant of retinal microvascular dysfunction.

Effect of smoking on the macula and optic nerve integrity using optical coherence tomography angiography

OBJECTIVE

To investigate the effect of chronic smoking on the macula and optic nerve integrity using optical coherence tomography angiography (OCTA).

METHODS

This prospective, comparative study involved the right eyes of 160 healthy subjects (80 smokers group, and 80 control group). OCTA scanning was performed for all subjects. All macular subfields thickness, peripapillary retinal nerve fiber layer (RNFL) thickness, macular ganglion cell complex (GCC) thickness, superficial and deep macular vessel density, foveal avascular zone (FAZ) area, and the macular outer retina flow area, were measured and analyzed.

RESULTS

The thickness of some macular subfields, inferior GCC, and RNFL was statistically significantly lower in the smokers' group (p < 0.05). The FAZ area was 0.409 ± 0.048 mm² in the smokers' group and 0.327 ± 0.055 mm² in the control group (p < 0.001). The superficial foveal VD was 31.35 ± 5.79% in the smokers' group and 33.63 ± 4.78% in the control group (p = 0.06). The deep foveal VD was 39.38 ± 4.56% in the smokers' group and 34.15 ± 6.57% in the control group (p ≤ 0.001). The superficial and deep parafoveal VD was 52.09 ± 4.56% and 59.99 ± 2.25% respectively in the smokers' group, and 54.75 ± 2.30% and 55.58 ± 4.69% respectively in the control group (p < 0.05). The macular outer retina flow area was 1.29 ± 0.12 mm² in the smokers' group and 1.16 ± 0.11 mm² in the control group (p < 0.001).

CONCLUSION

Chronic smoking affected the integrity of the macula and optic nerve. It decreased the macular VD, enlarged the FAZ, and increased outer retinal flow area.

RETINAL ARTERIAL DILATION IS IMPAIRED IN EYES WITH DRUSEN AND RETICULAR PSEUDODRUSEN

PURPOSE

To analyze static characteristics and dynamic functionality of retinal vessels in eyes with drusen and reticular pseudodrusen (RPD) using dynamic vessel analyzer.

METHODS

Patients with clinical diagnosis of isolated RPD or medium-large drusen and healthy controls were enrolled in the study between July 2016 and May 2018. Participants underwent complete ophthalmologic examination, including enhanced depth imaging structural optical coherence tomography, dynamic retinal vessel analysis, and static retinal vessel analysis.

RESULTS

Twenty-eight eyes of 23 patients with drusen (9 men, mean age 77 ± 6 years), 22 eyes of 16 patients with RPD (7 men, mean age: 76 ± 6 years), and 22 eyes of 22 control subjects (11 men, mean age of 75 ± 6 years) were enrolled. Static retinal vessel analysis did not show any significant difference between the three groups for the central retinal artery equivalent (P = 0.11), the central retinal vein equivalent (P = 0.27), and the arteriovenous ratio (P = 0.30). Dynamic vessel analysis showed significantly reduced arterial dilation in eyes with drusen (P = 0.0001) and RPD (P = 0.015) compared with control subjects. No significant difference was seen between drusen and RPD groups (P = 0.32). Dynamic vessel analysis of retinal veins showed no differences between the three groups (P = 0.10).

CONCLUSION

Dynamic vessel analysis in eyes with drusen and RPD revealed an impaired retinal arterial dilation in response to flicker light stimulation, which further supports the relationship between cardiovascular risk and age-related macular degeneration.

Longitudinal stability of retinal blood flow regulation in response to flicker stimulation and systemic hyperoxia in mice assessed with laser speckle flowgraphy

This study aimed to evaluate longitudinal changes in retinal blood flow in response to flicker stimulation and systemic hyperoxia in mice using a laser speckle flowgraphy (LSFG-Micro). The retinal blood flow in vascular area surrounding the optic nerve head was measured in 8-week-old male mice every 2 weeks until age 20-week. The coefficient of variation of retinal blood flow under resting condition was analyzed every 2 weeks to validate the consistency of the measurement. On day 1 of the experiment, retinal blood flow was assessed every 20 s for 6 min during and after 3 min flicker light (12 Hz) stimulation; on day 2, retinal blood flow was measured every minute for 20 min during and after 10 min systemic hyperoxia; and on day 3, electroretinography (ERG) was performed. Body weight, systemic blood pressure, and ocular perfusion pressure increased significantly with age, but the resting retinal blood flow and ERG parameters remained unchanged. Retinal blood flow significantly increased with flicker stimulation and decreased with systemic hyperoxia, independent of age. The LSFG-Micro provides consistent and reproducible retinal blood flow measurement in adult mice. Longitudinal assessments of retinal blood flow in response to flicker stimulation and systemic hyperoxia may be useful indexes for noninvasive monitoring of vascular function in retinas.

The Acute Effects of Electronic Cigarette Vaping and Tobacco Cigarette Smoking on Choroidal Thickness in Young, Healthy, Habitual, Dual Smokers

The present study aims to evaluate and compare the acute effects of tobacco cigarettes (TC) smoking and electronic cigarette (EC) vaping on foveal and choroidal thickness (CT) in young, healthy, dual smokers. Participants underwent four trials: 5 min TC; 5 min EC; 30 min EC; and 60 min nothing (sham trial). Scans before and immediately after each trial were obtained using spectral domain optical coherence tomography with the enhanced depth imaging mode. Changes in central foveal thickness (CFT), subfoveal choroidal thickness (SFCT), and CT at fourother points, 500 μm and 1000 μm temporally and nasally to the fovea, were measured. Forty-seven participants (33 male, 14 female; mean age 24.85 ± 1.57 years) were included. They smoked 13.53 ± 5.27 TCs/day for 6 ± 2.3 years and vaped ECs for the past 2.4 ± 1.08 years. We did not observe any statistically significant change in SFCT, CFT, and CT of the other points after any of the fourtrials. The acute changes in CFT and CT after EC vaping or TC smoking did not differ significantly compared to the sham trial. Smoking and vaping does not seem to result in statistically significant acute alterations in foveal and CT in young, dual smokers.

Retinal Neurovascular Coupling in Diabetes

Neurovascular coupling, also termed functional hyperemia, is one of the physiological key mechanisms to adjust blood flow in a neural tissue in response to functional activity. In the retina, increased neural activity, such as that induced by visual stimulation, leads to the dilatation of retinal arterioles, which is accompanied by an immediate increase in retinal and optic nerve head blood flow. According to the current scientific view, functional hyperemia ensures the adequate supply of nutrients and metabolites in response to the increased metabolic demand of the neural tissue. Although the molecular mechanisms behind neurovascular coupling are not yet fully elucidated, there is compelling evidence that this regulation is impaired in a wide variety of neurodegenerative and vascular diseases. In particular, it has been shown that the breakdown of the functional hyperemic response is an early event in patients with diabetes. There is compelling evidence that alterations in neurovascular coupling precede visible signs of diabetic retinopathy. Based on these observations, it has been hypothesized that a breakdown of functional hyperemia may contribute to the retinal complications of diabetes such as diabetic retinopathy or macular edema. The present review summarizes the current evidence of impaired neurovascular coupling in patients with diabetes. In this context, the molecular mechanisms of functional hyperemia in health and disease will be covered. Finally, we will also discuss how neurovascular coupling may in future be used to monitor disease progression or risk stratification.

Use of choroidal vascularity index for choroidal structural evaluation in smokers: an optical coherence tomography study

PURPOSE

To compare the choroidal vascularity index (CVI) and choroidal thickness (CT) in smokers and healthy non-smoking subjects using spectral-domain optical coherence tomography (SD-OCT).

METHODS

Forty-two smokers with no systemic disorders and 46 age-sex matched healthy volunteers were included in the study. SD-OCT was used to measure choroidal thickness at the fovea and 1500 µm intervals from the foveal centre in both nasal and temporal directions. Choroidal images were binarized and segmented to the luminal area (LA), stromal area (SA), and total choroidal area (TCA) using ImageJ software. The choroidal vascularity index was calculated as the ratio of LA to TCA. Smoking subjects were divided into three groups according to pack-year exposure: 10-20 pack-years, 20-30 pack-years, and >30 pack-years. Subgroup analysis was performed to evaluate the relationship between CT/CVI/LA/SA/TCA and pack-years.

RESULTS

The mean age of the smokers and non-smokers was 43.1 ± 7.26 years and 41.82 ± 9.92 years, respectively (p = 0.51). The mean subfoveal choroidal thickness was 301.57 ± 55.04 µm in smokers and 303.38 ± 53.42 µm in non-smokers (p = 0.826). No significant difference was observed between groups for CT values in the subfoveal location or at 1500 µm intervals in the nasal and temporal direction from the fovea. The CVI was significantly lower in smokers (65.4 ± 2.3%) than in non-smokers (66.3 ± 2.5%) (p = 0.021). In the subgroup analysis, subjects with >20 pack-years of smoking had a significantly lower CVI than non-smokers, but those between 10-20 pack-years did not. A negative correlation was found between the CVI and smoking, as measured by cigarette pack-years (r = -0.226, p = 0.04).

CONCLUSION

The CVI was significantly decreased in smokers compared to healthy controls. The study results suggest that the CVI could be a non-invasive tool for evaluating choroidal vascular changes in smokers.

Evaluation of the acute effects of cigarette smoking on the eye of non-Smoking healthy young male subjects by optical coherence tomography angiography

Purpose: Investigation of the acute effects of cigarette smoking on the eye using optical coherence tomography angiography (OCTA) on young healthy non-smoking male subjects.Materials and methods: The right eye of 25 healthy non-smoking male subjects were included in this study. Selected parameters of the macular and circumpapillary vasculature were measured, including macular flow indices, foveal avascular zone, vessel densities of macula and optic disc using OCTA. The measurements of the subjects were performed on the first day without smoking at 0 min, 5 min, 30 min and 60 min. Measurements were repeated at the same regime on the second day after smoking. Paired samples t-test and repeated measures one-way analysis of variance test was used for the statistical analysis.Results: The repeated measures analysis of variance test using the Bonferroni adjustment demonstrated a significant change for superficial and deep foveal vessel density, flow area of choriocapillaris, and circumpapillary capillary density following smoking (range of p value was <0.001-0.004). Intraocular pressure, foveal avascular zone area, flow area of outer retina and foveal non-flow area of superficial layer measurements did not have any significant changes following smoking (range of p value was 0.192-0.812).Conclusion: In non-smoking cases, even smoking only one cigarette significantly decreased the vessel density parameters at the acute period. Even though there was an increase in measured parameters shortly after smoking, it had lessened when compared to non-smokers, even one hour following smoking.

Evaluation of Foveal Avascular Zone and Capillary Plexus in Smokers Using Optical Coherence Tomography Angiography

Purpose:

To evaluate the macular microvasculature in smokers in comparison to healthy subjects using optical coherence tomography angiography (OCTA).

Methods:

Fifty chronic, regular smokers and 50 healthy non-smokers, as a control group, were recruited for the study. Foveal avascular zone (FAZ) area (mm²) and vessel density (VD) (%) in the superficial (SCP) and deep capillary plexus (DCP) were evaluated.

Results:

FAZ area was 0.424 ± 0.100 mm² in the smoker group and 0.333 ± 0.093 mm² in the non-smoking control group (P = 0.002). The deep foveal VD was 31.76 ± 6.33% in the smoker group and 53.09 ± 5.88% in the non-smoking control group (P = 0.006). Superficial foveal and parafoveal, deep parafoveal VD were not statistically different between the groups (P = 0.120), (P = 0.337), (P = 0.287), respectively.

Conclusion:

In our study, there was an enlargement of FAZ and reduction of foveal VD at DCP in the eyes of smokers compared with non-smoking adults.

The Effect of Smoking on Macular, Choroidal, and Retina Nerve Fiber Layer Thickness

Objectives

This study aimed to compare the thickness of the macula, choroid, and peripapillary retina nerve fiber layer (RNFL) in smokers with those of healthy, nonsmoking individuals using spectral domain optical coherence tomography (SD-OCT).

Materials and Methods

Sixty-eight healthy smokers with an average of 19.75 pack-years and 71 nonsmoker subjects (control group) were included in the study. Macular thickness, RNFL thickness, and choroidal thickness (CT) were measured by SD-OCT.

Results

The mean age of the smokers was 42.76±6.97 years and that of the control group was 41.15±11.61 years (p=0.32). Inferonasal and temporal RNFL thicknesses were 121.60±27.40 μm and 69.75±9.82 μm in the smokers group and 109.05±21.71 μm and 75.95±15.01 μm in the nonsmoker group, respectively. The differences were statistically significant (p=0.003, p=0.005, respectively). Central macular thickness (CMT) was 222.97±18.95 μm and subfoveal CT was 369.52±105.36 μm in the smoker group, while these values were 222.98±17.72 μm and 347.42±104.63 μm in the nonsmoker group, respectively. There were no significant differences in these comparisons (p=0.99, p=0.49, respectively). A significant negative correlation was found between smoking exposure and nasal and temporal CT.

Conclusion

The results of our study revealed that RNFL thickness was decreased but CMT and CT were not affected in healthy chronic smokers.

Looking into the eye of patients with chronic obstructive pulmonary disease: an opportunity for better microvascular profiling of these complex patients

Chronic obstructive pulmonary disease (COPD) is a complex disease with many patients suffering from cardiovascular comorbidity. However, cardiovascular diseases remain often undiagnosed in COPD. Assessment of the retinal microvasculature can provide value in cardiovascular profiling of these patients. Retinal microvascular assessment carried out via a noninvasive eye exam represents an easy to use tool when examining patients with COPD. The purpose of this review was to provide an overview of studies assessing structural and functional changes in the retinal microvasculature of patients with COPD. Findings demonstrated that structural and functional microvascular changes were more common and severe in COPD patients as compared to non-COPD controls, although few retinal investigations have been performed in patients with COPD. As cardiovascular comorbidities are highly prevalent in COPD, we advocate more research to investigate the value of an eye exam for microvascular phenotyping of COPD patients.

Effect of aging and lifestyle on photoreceptors and retinal pigment epithelium: cross-sectional study in a healthy Danish population

Photoreceptors and their supporting retinal pigment epithelium constitute the key functional parts of the retina. Here, a study was undertaken to show how aging and lifestyle factors affect the photoreceptor layer and the retinal pigment epithelium and Bruch's membrane complex (RPE-BM) in vivo in a healthy Danish population using spectral-domain optical coherence tomography. This was a cross-sectional study of healthy humans aged ≥50 years. All participants were interviewed for medical history and lifestyle factors. Maculae of all participants were scanned using spectral-domain optical coherence tomography. The thickness of the photoreceptor layer and the RPE-BM was measured on one eye from each participant. In 150 eyes of 150 participants, it was found that aging was associated with a decrease in the thickness of the photoreceptor layer (-0.143 μm/year, P = 0.031) and an increase in the thickness of the RPE-BM layer (0.100 μm/year, P = 0.029) at the foveal minimum. Regarding lifestyle factors, alcohol intake or BMI were not associated with any significant trend, but physical inactivity and smoking had effects on the photoreceptor layer (decreased thickness) and the RPE-BM layer (increased thickness) indicating an accelerated aging process of the macula. Taken together, aging affects photoreceptors and the RPE-BM, and these aging trends are accelerated in smokers and the physically inactive.

Cardiovascular risk factors as determinants of retinal and skin microvascular function: The Maastricht Study

Objective

Microvascular dysfunction is an important underlying mechanism of microvascular diseases. Determinants (age, sex, hypertension, dyslipidemia, hyperglycemia, obesity, and smoking) of macrovascular diseases affect large-artery endothelial function. These risk factors also associate with microvascular diseases. We hypothesized that they are also determinants of microvascular (endothelial) function.

Methods

In The Maastricht Study, a type 2 diabetes-enriched population-based cohort study (n = 1991, 51% men, aged 59.7±8.2 years), we determined microvascular function as flicker light-induced retinal arteriolar %-dilation and heat-induced skin %-hyperemia. Multiple linear regression analyses were used to assess the associations of cardiovascular risk factors (age, sex, waist circumference, total-to-high-density lipoprotein (HDL) cholesterol ratio, fasting plasma glucose (FPG), 24-h systolic blood pressure, and cigarette smoking) with retinal and skin microvascular function.

Results

In multivariate analyses, age and FPG were inversely associated with retinal and skin microvascular function (regression coefficients per standard deviation (SD) were -0.11SD (95%CI: -0.15;-0.06) and -0.12SD (-0.17;-0.07) for retinal arteriolar %-dilation and -0.10SD (-0.16;-0.05) and -0.11SD (-0.17;-0.06) for skin %-hyperemia, respectively. Men and current smokers had -0.43SD (-0.58;-0.27) and -0.32SD (-0.49;-0.15) lower skin %-hyperemia, respectively. 24-h systolic blood pressure, waist circumference, and total-to-HDL cholesterol ratio were not statistically significantly associated with these microvascular functions.

Conclusions

Associations between cardiovascular risk factors and retinal and skin microvascular function show a pattern that is partly similar to the associations between cardiovascular risk factors and macrovascular function. Impairment of microvascular function may constitute a pathway through which an adverse cardiovascular risk factor pattern may increase risk of diseases that are partly or wholly of microvascular origin.

Prediabetes and Type 2 Diabetes Are Associated With Generalized Microvascular Dysfunction

Background:

Type 2 diabetes (T2DM) is associated with an increased risk of cardiovascular disease. This can be partly explained by large-artery dysfunction, which already occurs in prediabetes (“ticking clock hypothesis”). Whether a similar phenomenon also applies to microvascular dysfunction is not known. We therefore tested the hypothesis that microvascular dysfunction is already present in prediabetes and is more severe in T2DM. To do so, we investigated the associations of prediabetes, T2DM, and measures of hyperglycemia with microvascular function measured as flicker light-induced retinal arteriolar dilation and heat-induced skin hyperemia.

Methods:

In the Maastricht Study, a T2DM-enriched population-based cohort study (n=2213, 51% men, aged [mean±standard deviation] 59.7±8.2 years), we determined flicker light-induced retinal arteriolar %-dilation (Dynamic Vessel Analyzer), heat-induced skin %-hyperemia (laser-Doppler flowmetry), and glucose metabolism status (oral glucose tolerance test; normal glucose metabolism [n=1269], prediabetes [n=335], or T2DM [n=609]). Differences were assessed with multivariable regression analyses adjusted for age, sex, body mass index, smoking, physical activity, systolic blood pressure, lipid profile, retinopathy, estimated glomerular filtration rate, (micro)albuminuria, the use of lipid-modifying and blood pressure-lowering medication, and prior cardiovascular disease.

Results:

Retinal arteriolar %-dilation was (mean±standard deviation) 3.4±2.8 in normal glucose metabolism, 3.0±2.7 in prediabetes, and 2.3±2.6 in T2DM. Adjusted analyses showed a lower arteriolar %-dilation in prediabetes (B=–0.20, 95% confidence interval –0.56 to 0.15) with further deterioration in T2DM (B=–0.61 [–0.97 to –0.25]) versus normal glucose metabolism ( P for trend=0.001). Skin %-hyperemia was (mean±standard deviation) 1235±810 in normal glucose metabolism, 1109±748 in prediabetes, and 937±683 in T2DM. Adjusted analyses showed a lower %-hyperemia in prediabetes (B=–46 [–163 to 72]) with further deterioration in T2DM (B=–184 [–297 to –71]) versus normal glucose metabolism ( P for trend=0.001). In addition, higher glycohemoglobin A1c and fasting plasma glucose were associated with lower retinal arteriolar %-dilation and skin %-hyperemia in fully adjusted models (for glycohemoglobin A1c, standardized B=–0.10 [–0.15 to –0.05], P <0.001 and standardized B=–0.13 [–0.19 to –0.07], P <0.001, respectively; for fasting plasma glucose, standardized B=–0.09 [–0.15 to –0.04], P <0.001 and standardized B=–0.10 [–0.15 to –0.04], P =0.002, respectively).

Conclusion:

Prediabetes, T2DM, and measures of hyperglycemia are independently associated with impaired microvascular function in the retina and skin. These findings support the concept that microvascular dysfunction precedes and thus may contribute to T2DM-associated cardiovascular disease and other complications, which may in part have a microvascular origin such as impaired cognition and heart failure.

Impact of combined hormonal contraceptives on vessels functionality

PURPOSE

To evaluate the dynamic and static retinal vascular functionality in young females using combined hormonal contraceptive (CHC).

METHODS

Thirty-eight consecutive young female subjects were enrolled in this study between January 2015 and December 2015. Subjects were divided in two groups: CHC group, defined as CHC use for ≥6 months, and control group, defined as no current and prior CHC use. Participants underwent a dynamic and static retinal vessel analysis using the Dynamic Vessel Analyzer (DVA, Imedos, Jena, Germany).

RESULTS

Seventeen subjects continuously took CHC for 54.6 ± 29.3 months, while 21 subjects belonged to control group. No difference was found between the CHC and control groups for age (p = 0.1), smoking status (p = 0.6), and systolic (p = 0.3) and diastolic (p = 0.1) blood pressure. With regard to dynamic analysis, women taking CHC exhibited a marked significant vasoconstriction following flicker stimulation in comparison with control group (-2.43 ± 2.5 vs 0.63 ± 2.1, respectively; p = 0.0002). No significant difference was observed between groups for mean arterial (p = 0.2) and venous dilatations (p = 0.3), arteriovenous ratio (p = 0.09), central retinal artery equivalent (p = 0.4), and central retinal venous equivalent (p = 0.5).

CONCLUSIONS

CHC may affect vessel reactivity to flicker light by increasing arteries constriction. This may reflect systemic changes in vascular functionality in subjects using CHC. Moreover, CHC should be considered as a confounding bias in studies involving DVA.

The Impact of Chronic Tobacco Smoking on Retinal and Choroidal Thickness in Greek Population

Aim. To investigate the effect of more than 25-year cigarette smoking on choroidal and retinal thickness, using spectral domain optical coherence tomography (SD-OCT). Methods. Thirty-one smokers and 25 age- and sex-matched nonsmokers, serving as control group, were submitted to slit-lamp biomicroscopy and dilated fundoscopy, SD-OCT, measurements of intraocular pressure (IOP), central corneal thickness (CCT), and axial length (AL). Heidelberg Spectralis was used to calculate choroidal thickness (CT), ganglion cell complex (GCC), outer retina layers (ORL), and macular thicknesses (MT). Results. The smokers' group consisted of 17 males and 14 females with mean age of 57.8 ± 4.5 years, while the controls' group consisted of 14 males and 11 females with mean age of 68.0 ± 4.1 years. CT and GCC thicknesses were significantly reduced in smokers compared to control group. The differences in thicknesses of ORL were marginally significant between two groups. The measurements of MT, IOP, CCT, and AL had the same distributions between smokers and nonsmokers. Conclusions. Tobacco smoking seems to result in thinner choroid and retina compared to nonsmokers. This is the first study in literature that investigates the anatomical effect of smoking for more than 25 years on the choroid and retina.

Effects of cigarette smoking on choroidal and retinal thickness and ocular pulse amplitude

BACKGROUND

In our study, we aimed to show the effects of smoking on choroidal thickness and ocular pulse amplitude. It is known that the anatomy and physiologic functions of the choroid is important in ocular diseases like glaucoma and age-related macular degeneration. Choroidal thickness is measured by the spectral domain optical coherence tomography (SD-OCT). The ocular pulse amplitude (OPA) is the difference between the systolic and diastolic intraocular pressure (IOP) and it is an index of choroidal perfusion.

DESIGN

This was a cross-sectional prospective observational study at the Turgut Ozal University Hospital setting.

PARTICIPANTS

The test subjects were divided into two groups: the smokers group which consisted in 24 participants (20 male, 4 female) and the control group with 22 participants (16 male, 6 female).

METHODS

The participants underwent full ophthalmological examination including best-corrected visual acuity (BCVA), spherical equivalent (SE) values of refractive errors, intraocular pressure (IOP), ocular pulse amplitude (OPA), central corneal thickness (CCT), axial length (AL) and choroidal thickness. The IOP and the OPA were measured with the dynamic contour tonometer. The CCT and the AL were measured with the Nidek AL-Scan (Nidek Co., Ltd., Gamagori, Japan). The choroidal thickness was measured by the Cirrus high-definition optical coherence tomography (Cirrus Version 6.0; Carl Zeiss Meditec, Dublin, CA).

RESULTS

Gender did not differ significantly between the groups (p = 0.12). The age, SE, IOP, OPA, CCT and AL did not differ significantly in smokers and control groups (p = 0.12, p = 0.37, p = 0.54, p = 0.80, p = 0.56 and p = 0.82, respectively). The nasal, temporal, central retinal (p = 021, p = 021, p = 0.11) and nasal, temporal, central choroidal thicknesses (p = 0.80, p = 0.39, p = 0.75) did not differ significantly between smokers and control groups.

CONCLUSIONS

We could not find a significant difference in OPA, retinal and choroidal thicknesses between smokers and non smokers. Further studies including histopathological changes in larger groups are needed to show the effect of smoking on choroidal thickness especially in patients with ocular diseases like age-related macular degeneration.

Retinal vascular calibre and response to light exposure and serial imaging

Purpose

To investigate whether retinal vessel calibre measurements on optical retinal photography are affected by light and dark exposure prior to photography and whether the vessel calibre changes during an imaging sequence of several images.

Methods

Digital optical retinal photographs were obtained from 32 healthy adults in two separate image sequences of six images during 1 min; one sequence with 10 min of dark exposure and one with 10 min of light exposure prior to imaging. Retinal arteriolar and venular calibres were measured computer-assisted and summarized as central retinal artery and vein equivalents (CRAE and CRVE). Outcome measures were difference in calibres after prior light versus prior dark exposure and difference in calibre during each of the two imaging sequences.

Results

CRVE was wider with prior light exposure (2.7%, p = 0.0001), comparing the first image in each image sequence. Within each sequence, there was a venular dilatation from first to last image, both with prior light exposure (1.7%, p = 0.0003) and prior dark exposure (3.1%, p < 0.0001), with the change less pronounced with prior light exposure (p = 0.0164). CRAE showed no significant change in either outcome.

Conclusions

Retinal venular calibre was wider with light exposure prior to imaging and increased slightly during the imaging sequences, less pronounced after prior light than dark exposure. Measurement error due to these effects will probably be reduced by avoiding dark prior to imaging, and a possible bias effect of endothelial dysfunction may possibly be reduced by measuring calibre on an image taken early in the image sequence.

Retinal vascular calibres are significantly associated with cardiovascular risk factors: the Tromsø Eye Study

PURPOSE

To describe the association between retinal vascular calibres and cardiovascular risk factors.

METHODS

Population-based cross-sectional study including 6353 participants of the Tromsø Eye Study in Norway aged 38-87 years. Retinal arteriolar calibre (central retinal artery equivalent) and retinal venular calibre (central retinal vein equivalent) were measured computer-assisted on retinal photographs. Data on blood pressure, body mass index (BMI), high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, glycosylated haemoglobin (HbA1c) and smoking were collected. Association between retinal vessel calibre and the cardiovascular risk factors was assessed by multivariable linear and logistic regression analyses.

RESULTS

Retinal arteriolar calibre was independently associated with age, blood pressure, HbA1c and smoking in women and men, and with HDL cholesterol in men only. Blood pressure had the strongest effect on arteriolar calibre, with a decrease in calibre of 3.6 μm (women)/4.1 μm (men) per standard deviation increase in mean arterial blood pressure. Retinal venular calibre was independently associated with age, blood pressure, BMI, HDL and LDL cholesterol and smoking in men and women. The effect of BMI and HDL cholesterol on venular calibre was sigifnicantly stronger in men than in women. Current smoking was the most important factor for venular calibre, where smokers had 13.2 μm (women)/15.2 μm (men) wider calibre than nonsmokers.

CONCLUSION

All the explored cardiovascular risk factors were independently associated with retinal vascular calibre, with stronger effect of HDL cholesterol and BMI in men than in women. Blood pressure and smoking contributed most to the explained variance.

Parafoveal retinal vascular response to pattern visual stimulation assessed with OCT angiography

We used optical coherence tomography (OCT) angiography with a high-speed swept-source OCT system to investigate retinal blood flow changes induced by visual stimulation with a reversing checkerboard pattern. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to quantify blood flow as measured with parafoveal flow index (PFI), which is proportional to the density of blood vessels and the velocity of blood flow in the parafoveal region of the macula. PFI measurements were taken in 15 second intervals during a 4 minute period consisting of 1 minute of baseline, 2 minutes with an 8 Hz reversing checkerboard pattern stimulation, and 1 minute without stimulation. PFI measurements increased 6.1±4.7% (p = .001) during the first minute of stimulation, with the most significant increase in PFI occurring 30 seconds into stimulation (p<0.001). These results suggest that pattern stimulation induces a change to retinal blood flow that can be reliably measured with OCT angiography.

The age-related maculopathy susceptibility 2 polymorphism and polypoidal choroidal vasculopathy in Asian populations: a meta-analysis

OBJECTIVE

To assess the role of the age-related maculopathy susceptibility 2 (ARMS2) A69S polymorphism as a risk factor for polypoidal choroidal vasculopathy (PCV) in Asian populations.

METHODS

We performed a meta-analysis of the association of the A69S variant with PCV in Asian populations using data available from 14 case-control studies involving 6552 subjects. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using fixed- and random-effects models. Sensitivity analysis also was performed.

MAIN OUTCOME MEASURES

Understanding the relationship between the A69S variant and PCV is essential to provide new insights into pathophysiology and potential targets for intervention of PCV.

RESULTS

The pooled OR in random-effects models for genotype TG+TT versus wild homozygous genotype GG is 2.39 (95% CI, 1.98-2.89), the OR of heterozygous genotype TG versus GG is 1.66 (95% CI, 1.37-2.00), the OR of homozygous genotype TT versus GG is 4.74 (95% CI, 3.94-5.70), and the OR of allele T versus G is 2.14 (95% CI, 1.79-2.56). A sensitivity analysis indicated the robustness of our findings.

CONCLUSIONS

Our analysis provides evidence that the A69S variant is associated with an increased risk of PCV in Asian populations. The variant of A69S could be a promising genetic biomarker of PCV.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Effects of hyperbaric oxygen on crystalline lens and retina in nicotine-exposed rats

OBJECTIVE

To determine histopathological changes on crystalline lens and retina of rats after subcutaneous injection of nicotine and to examine the effects of hyperbaric oxygen (HBO) on these changes related to nicotine exposure.

METHODS

Twenty-eight female Sprague-Dawley rats were enrolled in the study and the rats were divided into four equal sized groups randomly (Group N: the rats exposed only to nicotine, group HB: the rats received only HBO, group N+HB: the rats that underwent to nicotine injection and subsequently received HBO, group C: the control group that neither exposed to nicotine nor received HBO). The rats were sacrificed by decapitation method and all were enucleated immediately after scarification. Tissue samples from crystalline lens, lens capsule, and the retina from the right eyes of the rats were examined by light microscopy.

RESULTS

While the histological appearances of the retina and the lens was similar in group HB, group N+HB, and the control group; group N showed some pathological changes like decrement in the retinal ganglion cell density, atrophy of the retinal nerve fiber layer, congestion of the vessels in the optic nerve head, thinning of the internal plexiform layer, thinning of the lens capsule, and transformation of the anterior subcapsular epithelium into squamous epithelia.

DISCUSSION

Subcutaneous injection of nicotine was found to be related with some pathological changes in the retina and lens of the Sprague-Dawley rats. However HBO caused no significant negative effect. Furthermore, the histopathological changes related to nicotine exposure in the lens and retina of the rats recovered by the application of HBO.